Method and apparatus for making magnetically anisotropic permanent magnets



METHOD AND APPARATUS FOR MAKING MAGNETICALLY ANISOTROPIG PERMANENT MAGNETS Filed Dec. 18, 1962 Sept. 20, 1966 w. MULLER 3,274,303

INVENTOR WERNLR MULLER United States Patent 3,274 303 METHOD AND APPARATUS FOR MAKING MAG- NETICALLY ANISOTROPIC PERMANENT MAG- NETS Werner Miiiler, Bad Godesberg, Germany, assignor to Magnetfabrik Bonn Gewerkschaft Windhorst, Bonn, Germany Filed Dec. 18, 1962, Ser. No. 245,610 Claims priority, application Germany, Dec. 21, 1961, M 51,256 3 Claims. (Cl. 26424) The invention relates to a method and apparatus for making magnetically anisotropic permanent magnets.

Such permanent magnets are prepared by compressing finely divided ferromagnetic material in a molding die to the desire shape while at the same time orienting the fine particles under the influence of a magnetic field so as to impart magnetically anisotropic properties to the shaped body. This preparation method is well known and described for instance, in Patent Nos. 2,188,091 and 2,762,778.

It is a principal object of the invention to provide a method to improve the orientation of the magnetic particles prior to the compacting operation.

Other objects and advantages will be apparent from a consideration of the specification and claims.

The invention consists essentially in providing means to preorient the magnetic particles during a loosening action which makes the particles better capable of responding to magnetic orientation.

For a more detailed description of the invention, reference is made to the accompanying drawing showing, by way of example, diagrammatically a suitable apparatus for carrying out the method of the invention.

In the drawing,

FIG. 1 is an elevational view, partly in section, of a compacting and magnetizing apparatus at the beginning of the orienting and compressing operation,

FIGS. 2 and 3 show the apparatus in intermediate stages of the operation, and

FIG. 4 shows the apparatus in its end position, the magnetic powder being compacted in oriented position of the particles.

Referring now to the drawings, the numeral 1 represents the mold of non-magnetic or slightly magnetic material of a press, with a lower die 2 and an upper die 3 of magnetic material, for instance steel. Magnetizable powder 4 of the type described in the patents referred to above is placed into the mold only to such an amount as to fill only part of the cavity. The mold is surrounded by a magnetizing winding 5 which, when passed by an electric current, produces a magnetic field inside the mold. The upper die 3 is also surrounded by a magnetizing winding 6, which can be connected to a source of direct current independently of the winding 5.

A magnetically anisotropic permanent magnet is then obtained as illustrated in FIGS. 2 to 4. In FIG. 2, both magnetizing windings are still inoperative, and the upper die 3 is lowered close to the surface of the molding powder. In said instant, the upper die 3 is magnetized by flowing a current through the winding 6, and raised at the same time. Hereby, also the powder is magnetized and the loose particles are drawn out filament-like to fill the entire expanded space between the upper and lower die, as illustrated by the numeral 7 in FIG. 3. Then, the coil 5 is energized and the compacting operation is started by forcing the die 3 downwardly (FIG. 4). Thereby, the oriented patricles of the magnetic powder retain substantially their orientation so that also the compacted body 8 is magnetically oriented. Said body is then removed from the mold and finished, by sintering, if it is prepared from a magnetic powder, or by calcination, if a ceramic powder is used.

It will be seen that the invention consists essentially in providing the upper die of the press with a separate magnetizing coil; the die is first lowered on the molding powder in the unenergized state; when in the lowest position, the coil is energized and the die is raised, and finally also the conventional magnetizing coil of the mold is energized, and the molding powder is compacted by lowering the upper die again.

The process of the invention may be used for the manufacture of round or angular discs, or rings or magnetic bodies of other shapes. It is particularly suitable for making permanent magnets from materials having high coercivity such as barium ferrite. The process allows also the preparation of press magnets from a magnetic powder and a binder which hardens when subjected to pressure and heat.

I claim:

1. A method of making magnetically anisotropic permanent magnets comprising subjecting a powder of a permanent ferromagnetic material placed in a confined space to a magnetic force which lifts particles of said magnetic powder so as to expand said powder and render said particles more mobile, then applying a magnetic field across said expanded powder, thereby orienting said particles while in said mobile condition, and finally compacting said powder in said confined space while said magnetic field is applied.

2. In an apparatus for making magnetically anisotropic permanent magnets, a molding die comprising a substantially non-magnetic sleeve, a lower and an upper ram entering said sleeve to compact magnetic powder placed therein, said upper ram being vertically displaceable and made of a magnetic material, a magnetizing coil around said sleeve, a magnetizing coil around said ram, and means energizing said coils with direct current separately and independently from each other.

3. A method of making magnetically anisotropic permanent magnets comprising placing a powder of permanent feromagnetic particles in a die cavity between an upper and a lower ram, lowering said upper ram close to the surface of said powder, magnetizing said upper ram so as to magnetically attract said particles, then raising said upper ram to expand and loosen up said powder, subsequently, applying a direct magnetic field across said expanded powder so as to orient said particles, and finally lowering again said upper ram to compact said powder while the particles are oriented.

References Cited by the Examiner UNITED STATES PATENTS 2,188,091 1/1940 Baermann 264-24 2,384,215 9/ 1945 Toulmin.

2,43 7,127 3/1948 Richardson.

2,999,271 9/1961 Falk et al 29155.59 XR ROBERT F. WHITE, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

M. R. DOWLING, Assistant Examiner. 

1. A METHOD OF MAKING MAGNETICALLY ANISOTROPIC PERMANENT MAGNETS COMPRISING SUBJECTING A POWDER OF PERMANENT FERROMAGNETIC MATERIAL PLACED IN A CONFINED SPACE TO A MAGNETIC FORCE WHICH LIFTS PARTICLES OF SAID MAGNETIC POWDER SO AS TO EXPAND SAID POWDER AND RENDER SAD PARTICLES MORE MOBILE, THEN APPLYING A MAGNETIC FIELD ACROSS SAID EXPANDED POWDER, THEREBY ORIENTING SAID PARTICLES WHILE IN SAID MOBILE CONDITION, AND FINALLY COMPACTING SAID POWDER IN SAID CONFINED SPACE WHILE SAID MAGNETIC FIELD IS APPLIED. 